1. Field of the Invention
The present invention relates to fuel cell systems and more particularly to a leakage-proof valve structure that prevents leakage of liquid fuel during replenishment of the fuel cell unit in the fuel cell system with liquid fuel from a fuel cartridge.
2. Description of the Related Art
Conventionally, a fuel cell system includes a fuel cell unit containing a fuel cell module that produces electrical energy from liquid fuel, and a fuel cartridge containing liquid fuel for supplying the fuel cell unit with fuel. Fuel is supplied from the fuel cartridge to the fuel cell unit through a valve mechanism that is composed of two valves respectively provided to the fuel cell unit and the fuel cartridge, part of one valve being inserted into the other to establish fluid communication.
One type of known fuel cartridge for such a fuel cell system has a valve mechanism at one end of the container body that contains injection material such as compressed fluid with fuel. The valve mechanism has a fuel supply passage, and a stem arranged through the passage is pushed in to open the valve and to enable fuel injection through the fuel supply passage (see, for example, Japanese Patent Laid-Open Publication No. 2005-5155).
FIG. 5A and FIG. 5B illustrate a valve mechanism that is commonly used for such fuel cell system: A pair of valves are connected with each other to enable fuel supply, and disconnected from each other to stop the fluid communication. As shown, the valve mechanism generally is composed of a male valve 41 and a female valve 51 that receives the distal end of the male valve 41. The male valve 41 contains a valving element 43 that forms part of a valve seal 42, with a stem 44 extending from the valving element 43 towards the distal end. The male valve 41 further includes a flange 45 that surrounds the female valve 51 when they are connected, and a sealing member 45a arranged in the inner circumference of the flange. The female valve 51 has an inner space 55 at the distal end to receive the male valve 41, a valving element 53 that forms part of a valve seal 52, and a stem 54 extending from the valving element 53, the distal end of the stem 54 being positioned in the inner space 55. When the stem 44 of the male valve 41 abuts on the stem 54 of the female valve 51, the valving element 43 is pushed in and the valve seal 42 is opened. Similarly, when the stem 54 of the female valve 51 abuts on the stem 44 of the male valve 41, the valving element 53 is pushed in and the valve seal 52 is opened. Which one of the valve seals 42 and 52 is opened first depends on the force of the springs 46 and 56 that press the valve seals 42 and 52, respectively. In the illustrated example, the force of the spring 56 of the female valve 51, from which fuel is supplied, is stronger.
In this valve mechanism, when the valves 41 and 51 are not connected, both valve seals 42 and 52 are closed, as shown in FIG. 5A. As the male valve 41 is inserted into the inner space 55 of the female valve 51, the flange 45 of the male valve 41 fits on the female valve 51, with the sealing member 45a providing a seal between the inner surface of the flange 45 and the outer surface of the female valve 51. Then the stem 44 of the male valve 41 is pushed by the stem 54 of the female valve 51 because the force of the spring 46 is weaker than that of the female side, whereby the valving element 43 is pushed in and the valve seal 42 is opened. As the male valve 41 is inserted further into the inner space 55 of the female valve 51, the stem 54 of the female valve 51 is pushed by the stem 44 of the male valve 41, and the valving element 53 is pushed in to open the valve seal 52. Both valves 41 and 51 are thus opened, and fuel is supplied from the female valve 51 to the male valve 41. In FIG. 5B, the male valve 41 is completely inserted into the inner space 55 of the female valve 51. When the valves 41 and 51 are disconnected, the above-described process takes place in the reverse order, i.e., the supply-side female valve 51 is closed first, and then the male valve 41 is closed, after which the sealed space formed by the sealing member 45a between both valves 41 and 51 is opened up.
This valve mechanism shown in FIG. 5A and FIG. 5B has the following problem when applied to the connection between the fuel cell unit and the fuel cartridge: After the fuel supply, before both valves 41 and 51 are separated, with the valve seals 42 and 52 being closed, some fuel remains in the fuel supply passage that is formed between the valve seals 42 and 52 including the gap between the inner space 55 of the female valve 51 and the male valve 41. When the valves 41 and 51 are completely separated from each other, this remaining fuel leaks out, particularly from the inner space 55 of the female valve 51. The same problem occurs with the valve mechanism described in Japanese Patent Laid-Open Publication No. 2005-5155.
Since the most preferably used methanol fuel for fuel cells is harmful to human bodies, especially eyes, any leakage, even in a slight amount, in a place where human hand contact is possible, is considered impermissible. The possibility of adverse effects is reported even with more than 0.2 cc per 10 kg body weight. Fuel cell units are used for various portable electronic devices which a small child may touch and therefore fuel leakage must absolutely be eliminated. The above valve mechanisms clearly fail this requirement.
End seal valves are being considered, which provide a seal between male and female valves by a contact between the distal end of the male valve and sealing means arranged in the inner space of the female valve, but a new valve mechanism that eliminates leakage to a sufficient extent is yet to be developed.